The molecular evolution of conifers was elucidated by using DNA sequence information on chloroplast DNA and/or 18S rDNA gene on nuclear DNA. The main results are as follows:1.Phylogeny of conifer at family level: The DNA sequences (ca, 3,000 bps) of three chloroplast DNA genes, atpA, petA and rbcL were decided in eight coniferous families. A new finding that was different from the traditional hypothesis was revealed from maximum likelihood analysis of sequence information.2.Phylogeny of the family Cupressanceae: The DNA sequence of the three above-mentioned genes was decided in 11 genera. Chamaecyparis nootkatensis which had been included to the genus Chamaecyparis up to now was classified into the genus Cupressus. In addition, the 18S rDNA sequences of six species in Chamaecyparis was decided. These species can identify using a specific sequence.3.Evolution of the family Pinaceae: The DNA sequences of six genes (atpA, petA, rbcL, rpoA, rps2 and rps3) on chloroplast DNA were decided for nine genera which composed the Pinaceae. The Phylogeny of the family was analyzed based on the sequence information. As a result, the family Pinaceae was classified into four subfamilies.4. The construction of a new classification system in the genus Pinus: In Pinus, the largest taxon in the conifer, the classification system based on the phylogeny was restructured from chloroplast DNA information. A molecular phylogenetic tree was made from DNA information of three genes (atpA, rbcL and rpoA) on chloroplast DNA. A new classification system which was greatly different from the traditional classification systems was proposed based on this tree. Four sections and 11 subsections of the new system were composed of the species which were distributed in the neighborhood. The biogeographic factor strongly influenced the evolution of the Pinus.